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This report properly constitutes a part of the records of the
expedition of the California Academy of Sciences of 1925 to
various west Mexican islands.^ The collecting of marine mol-
lusca was placed in the hands of Eric K. Jordan and G. D.
Hanna who had a special request from Dr. W. H. Dall to do
the task as thoroughly as possible at Clarion and Socorro
islands. It appears that no previous visitors to these little-
frequented places had brought back more than a scattering of
shells and these were not sufficient to permit the detennination
of the relationships of the group. Indeed, Dr. Dall was led
to suppose from the few he had seen from Clarion Island’ that
an Indo- Pacific fauna was dominant there. Stearns^ in 1894
stated that: “Of Socorro, the principal island of the more
distant Revillagigedo group, we know but little or nothing.
It was visited several years ago by Grayson, the ornithologist.

For a general account of this expedition, see Proc. Calif. Acad. Sci., ser. 4, vol. 15, no. I, pp. 1-113, pis. 1-10, text figs. 1-7, March 30, 1926. Various technical reports based upon the collections obtained have appeared subsequently.”